Fresnel lens.



W. CHURCHILL. FRESNEL LENS. APPLICATION FILED mum, 191s.

Patented Dec. 9, 1913.

2 SHEETSSHBET 1.

W. CHURCHILL.

FRESNEL LENS.

APPLICATION FILED mums. 1913.

1,081,210, Patented De0.9, 1913.

2 SHEETSSHEET 2.

the center of curvature of the bounding cir- UNITED STATES PATENT OFFICE.

WILLIAM CHURCHILL, OF CORNING, NEW YORK, ASSIGNOR TO CORNIN G GLASS WORKS, OF CORNING, NEW YORK..

FRESN EL LENS.

Application filed March 6, 1913} Serial No. 752,424.

design is that the light emanating from the source of illumination is concentrated with higher intensity along the axial planes bisecting the angular surfaces at right angles. There is+see Fig. 2 of my said patenta corresponding diminution of intensity along similar axial planes passing through the lines of intersection of the rectangular surfaces. The main advantage of a lens so c011- structed is, as stated in the said patent, that owing to the higher intensity of the beams in certain planes the range of the light is materially increased along the lines of maximum intensity, and a diminution of intensityjn the alternate intervals is not detrimental for the reason that since the light to be observed is usually on a vessel or other moving object in more or less continual motion, and the observer is frequently also upon a vessel or other moving object,- the motion in various directions will bring the regions of higher intensity within the range of the observer about as often as are brought to it the regions of diminished intensity, thereby producing an effect approximating to a greater or lesser extent to that of a flashlight.

To all whom zit may concern:

Be it known that I, WILLIAM CHURCHILL, a citizen of the United States, residing at Corning, in the county of Steuben and State of New York, have invented new and useful Improvements in Fresnel Lenses, of which the following is a specification.

Iy invention relates to an improvement in the socalled Fresnel type of lens.- generally used in marine service for sidelights and mast-head lights, also for signal lights upon drawbridges over navigable rivers in conformity with the regulations of the United States Lighthouse Service and occasionally in railroad service for special lamps.

The designation Fresnel is commonly confined to lenses consisting of a hollow cylinder of glass or section of a cylinder with corrugations arranged transversely on the outer face, the cylinder or section having a smooth outer face. Such lenses are constructed either by building up a series of separate ground and polished segments of glass held in place by a metal frame, or else the entire lens is pressed in one solid piece in a metal mold. The latter is obviously the less expensive method and the one gen'- erally followed where extreme accuracy is not essential. I

Lenses of the Fresnel type concentrate the light impinging upon them in a fan shaped beam spreading with approximately equal intensity, to all points of the compass covered by the cylinder or section of a cylinder. They are generally placed in lamps so that the cylinder or section stands upright, the prismatic corrugations acting to condense the rays in all planes parallel to the axis of the'cylinder, but having no condensing effect in planes perpendicular to the axis.

In my Patent No. 849,977, dated April 9, 1907, is covered an improvement in Fresnel lenses which may be described as follows: The inner cylindrical surface of the lens is made .to consist of a series of connected rectangular planes, angularly disposed with respect to each other, each, of the said, planes being tangential to an inner circle which is concentric with the outer bounding-circle of the lens, thereby forming the inner surface of the lens and producing in cross section a polygonal figure, the center of which is ."a lens of the Fresnel type capable of projecting a series. of relatively concentrated beams as described in mysaid Patent No..849,977, but having a relatively smooth outer face instead of the series of horizontal prisms usually found' on a fresnel. Thus, assuming my present invention to be directed to a lens of the Fresnel type for railroadservice, as for example in a classification lamp carried at the head end of a locomotive, Idispose the corrugations which produce concentraltion in the vertical plane'upon the inner surface of the lens instead of upon its outer face, and form the outer face of the lens of form of cylindrical.

a series of panels in the segments some or all of which have a radius of curvature less than the distance from the source of illumination to the inner face of the lens. These segments being portions of a cylinder necessarily have parallel outlines or sides. I thus produce a lens free from corrugations on the outer face and yet-one possessing the advantage to be derived from the condensation of the light in a series of relatively intense beams. A great advantage of the smooth outer face is cle. The optical result produced by such Patented Dec. 9, 1913. I

For certain purposes it is desirable to have that the lens canfying the design to meet the special requirements of any given case it is possible to secure any desired distribution of the light within the several beams.

much more easily be kept clean, there being practically no opportunity for dust and dirt to lodge on the exposed outer face.

In the accompanying drawing, Figure 1 is a view of my lens in perspective. Fig. 2 18 My invention may be modified b using a section throu h the center of one of the segmental panels of varying radii o curvasegmental panefs, in other words, as along ture on the outer face, or by combining such the radial line AH as shown in Fig. 3. panels of relatively shorter curvature with Fig. 3 is a top view, and illustrates the acothers having a center of curvature coin tion of the lens in producing a series of ciding with the source of illumination and beams. Figs. t and 5 show modifications the sweep of the prisms on the inner face. hereinafter described. Thus if it be desired to produce a concen The panels referred to are indicated in trated beam along the axis AJ of Fig. 3, a the several embodiments of my invention single segmental panel, 5, as seen in Fig. 4:, by 1, 2, 3, 4 and 5. In Fig. 3 the planes may be substituted for the panels 2 and 3 of of maximum intensity are indicated respec- Fig. 3; or, as shown in Fig. 5, the radius tively by the radial lines AD, A.- of curvature A- Y asseen in Fig. 8 may A-L, and AP. The planes of minimum be used for the outer face between the points intensity are shown by the lines A-B, X and Z at the inner sides of the panels 1 A-F-, A-J, AN, and A-R. Accordand l, respectively. In the latter case the ingly the angles A- E, A-GI, segment A-XZ would act as an ordinary A-K M and AOQ are those covered Fresnel lens having on each side a beam 0 by the beams of higher intensity, while the relatively h'gh intensity produced by the angles AEG, A-I--K, means described. r\-M-O and AQ-R are those covered A lens designed and constructed according by beams of diminished intensity. It is to my invention may be made to cover any racticable to design and construct the lens angle up to 360 degrees. However, if the so that bet-ween ,the beams of high intensity angle covered exceeds 180 degrees it is necesthere are intervals of total darkness. sary to press the lens in two or more parts this result is desired a relatively small numand then combine them by cement, metal fittings or other suitable means.

her of such segmental panels are provided, this modification requiring that the angle covered by each segment shall be made relatively large and the radius of curvature relatively short. I have, however, found it desirable, in most cases, to employ segmental anels of such size and curvature that with an. ordinary source there shall be some illumination at every point of the angle which the lens subtends. It is entirely practicable to obtain such a result, for the series of fan-like beams-projected by the lens tend to overlap at their edges. If the source of illumination employed were intensely concentrated so that it approximated a mathematical point, such overlapping of the Having thus described my invention, I claim 1. A Fresnel lens the outer surface of which is provided with a series of connected segmental panels each having a radius of curvature less than the radius of curvature of the cylinder passing through the points of intersection of said panels, substantially as set forth.

2. A Fresnel lens the outer surface of 1 which is provided with a series of connected segmental panels each having a radius of curvature common to all and less than the radius of curvature of the cylinder passing through the points of intersection of said 1 beams would obviously be practically impanels, substantially as set forth. possible, and therefore in a lens designed 3. A. Fresnel lens the outer surface of according to my invention we should have a which is provided with segmental panels each having a radius of curvature less than the radius of curvature of said outer surface, substantially as set forth.

In testimony whereof I afiix my signature in presence of two witnesses.

WILLIAM GHUR CHILL.

Witnesses HENRY PHELPS GAGE, EMILIO PASCUCOI.

series of zones of total darkness alternating with the zones of maximum illumination. However, with the sources employed in ordinary practice such an efiect, though not necessary, can be produced or avoided as may be desired. \Vith the relatively large area covered by a kerosene flame, or an ordinary incandescent lamp filament, the two mostcommon sources of illumination in lamps where fresnels are employed, by modi- 

